本文為大家分享了Java實現文件上傳下載功能的具體代碼，供大家參考，具體內容如下
前端通過form表單的enctype屬性，將數據傳遞方式修改為二進制”流“的形式，服務端（servlet）通過getInputStream() 獲取流信息， 運用java I/O 流的基礎操作將流寫入到一個服務端臨時創建的文件temp中，然後再次利用文件基本操作，讀取並截取臨時文件內容，根據其中信息創建相應的文件，將讀取出來的具體信息寫入，下載時，根據提交的文件名稱，找到服務器端相應的文件，然後根據輸出流outStream輸出到頁面，同時將servlet的響應類型和響應頭進行設置。
具體傳輸流程如下圖：
流信息的部分為：
具體代碼如下：
前端代碼：
<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>Insert title here</title><script src="Js/jquery.js"></script></head><body> <form action="FileUpServlet" method="post" enctype="multipart/form-data"> <table> <tr> <td>請選擇上傳文件:</td><td><input id="myfile" name="myfile" type="file" value="" /></td> <td><input type="submit" value="上傳"></td> </tr> <tr><td>${info}</td></tr> </table> </form> 文件下載：<a href="FileLoadownServlet?filename=${filename}">${filename}</a></body></html>上傳servlet部分（核心）
@WebServlet("/FileUpServlet")public class FileUpServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public FileUpServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub doPost(request, response); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub request.setCharacterEncoding("utf-8"); InputStream filesource = request.getInputStream();//request獲取流信息String tempname = "D:/temp";//tempfile代表臨時存放文件File tempfile = new File(tempname);//創建臨時文件FileOutputStream outputStream = new FileOutputStream(tempfile);//輸出流對象，指定輸出指tempfile目錄下byte b[] = new byte[1024]; int n; while((n = filesource.read(b))!= -1)//從輸出流中每次讀取1024字節,直至讀完{ outputStream.write(b,0,n); } outputStream.close(); filesource.close();//關閉輸入輸出流/*以下為具體的文件操作，主要為解析臨時產生的temp文件，知識多為java輸入輸出流的內容！ */ RandomAccessFile randomfile = new RandomAccessFile(tempfile, "r");//隨機流，指定要讀臨時文件，只讀randomfile.readLine();//讀取第一行,無效數據，不需要String str = randomfile.readLine();//讀取第二行int beginIndex = str.lastIndexOf("=")+2;//指定所需數據的開始位置int endIndex = str.lastIndexOf("/"");//指定所需數據截至位置String filename = str.substring(beginIndex,endIndex);//截取文件名//重新定位文件指針，獲取文件內容randomfile.seek(0);//文件指針從頭開始long startext = 0; int i = 1; //文件內容開始位置while((n=randomfile.readByte()) != -1&&i <= 4) { if(n=='/n') { startext = randomfile.getFilePointer(); i++; } } startext = randomfile.getFilePointer() - 1; //獲取文件內容結束位置randomfile.seek(randomfile.length()); long endtext = randomfile.getFilePointer(); int j = 1; while(endtext >= 0 && j <= 2) { endtext--; randomfile.seek(endtext); if(randomfile.readByte()=='/n') { j++; } } endtext = endtext-1; //將臨時文件保存至指定目錄中String realpath = getServletContext().getRealPath("/")+"images";//設置文件保存目錄System.out.println(realpath); File fileupload = new File(realpath); if(!fileupload.exists()) { fileupload.mkdir();//目錄不存在則創建} File savefile = new File(realpath,filename); RandomAccessFile randomAccessFile = new RandomAccessFile(savefile, "rw"); randomfile.seek(startext); while(startext<endtext){ randomAccessFile.write(randomfile.readByte());//文件寫入startext = randomfile.getFilePointer(); } //關閉各種輸入輸出流randomAccessFile.close(); randomfile.close(); tempfile.delete();//刪除臨時文件SimpleDateFormat timed = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date nowdate = new Date(); String time = timed.format(nowdate.getTime()); request.setAttribute("info", time+" "+filename+"上傳成功！"); request.setAttribute("filename", filename); request.getRequestDispatcher("/fildeOp.jsp").forward(request, response); }}下載部分
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub String filename = request.getParameter("filename"); String path = getServletContext().getRealPath("/")+"images/"; File file = new File(path+filename);//找到文件if(file.exists()) { response.setContentType("application/x-msdownload"); //設置響應類型,此處為下載類型response.setHeader("Content-Disposition", "attachment;filename=/""+filename+"/"");//以附件的形式打開InputStream inputStream = new FileInputStream(file); ServletOutputStream outputStream = response.getOutputStream(); byte b[] = new byte[1024]; int n; while((n = inputStream.read(b)) != -1) { outputStream.write(b,0,n); } outputStream.close(); inputStream.close(); }else{ request.setAttribute("result", "文件不存在！下載失敗！"); request.getRequestDispatcher("/fildeOp.jsp").forward(request, response); } }以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。